GSXR 750 1990 front end swap?

[Rob21]

Been searching across different sites about swapping modern forks into the yokes. Want to use radial calipers and 320 discs with better suspension. Thing is my bike has a custom top yoke with risers for fat bars all made to standard 750 1990 spec. I would like to keep this if possible? I've thought about sliding in k6 forks into the standard yokes and using different wheels/spacers to make up and clearance? Any advice would be appreciated, can give pics /  dimensions if needed. Cheers

[no class]

search "fork matrix" ......perhaps some others out there on the spider web .

[SiBag]

If you swap to later forks you may have to change the wheel due to the larger dia spindle. Or some funky tophats.

 

[colinworth79]

I managed to run a bandit wheel in k4 forks but had a spindle made up . Later front end have forks closer together so think you will have to use the yokes with the forks . Late gsxr front ends will drop in with just a bearing change , then run the 600 5.5 inch rim in the rear to match . Later wheels lot lighter than slingshot stuff but more easily damaged so be careful when buying off that site .

[Jaydee]

1 hour ago, SiBag said:

If you swap to later forks you may have to change the wheel due to the larger dia spindle. 

 

Done plenty of mix'n'match front ends. You can get around this in most cases with a bearing swap and new matching crush tube to go between the bearings. For example, a slingshot wheel has a 6204 bearing (47x20x14) which can be swapped for a 6005 bearing (47x25x12). It won't matter that the new bearing is a little slimmer than original as you will have to make custom spacers to center the wheel in the forks. 

Anything is possible when it comes to mixing forks, yokes and wheels. I have a front end made up of K3/4 radial forks and calipers, 320mm flat discs and axle, slingshot 750 yokes and wheel. I had to make a few parts to get this all to work such as spacers/adapters for mating k series discs to slingshot wheel, spacers for the calipers, spacers for aligning the front wheel and axle locknut with new threads 7mm further out than original to allow for the forks now being 214mm as opposed to K series 207mm centers.

Here's the fork matrix if you can't find it.  

[Rob21]

Thanks for the replies

 

Sounds good Jaydee! better performance over spending money on the standard forks and brakes?

May need to get some dimensions off of yourself when it comes to piecing together a front end?  Cheers. 

[Jaydee]

21 minutes ago, Rob21 said:

Thanks for the replies

 

Sounds good Jaydee! better performance over spending money on the standard forks and brakes?

Should be. Haven't on the road yet as it's a current mid-build project but have the front end done for ages. 

 

24 minutes ago, Rob21 said:

May need to get some dimensions off of yourself when it comes to piecing together a front end?

Not a problem. I have detailed tech drawings with all the measurements.

*Now even though I carefully measured, planned in every meticulous way when designing the parts, the front wheel was 1.5mm to the left. Not a problem, just remade the spacers to suit the proper re-alignment. Once I did that, everything lined up, discs where bang on centered to the radial calipers. . Small bit of trial and error in setting up. But that's always the way when truing up a front or rear end for that matter. 

[dupersunc]

750m forks are pretty good in my experience.  Even the brakes are ok. Best improvements would be from  a decent master cylinder and lighter wheels.

[Rob21]

Nice one Jaydee, you got a build log going? Really intrigued.

 

I have a brembo rcs 19 hooked up, massive improvement, want more though haha. I just don't want to throw ktech piston kit and springs at the forks and change discs, maybe callipers where I could have pieced a front end of modern stuff with more scope of upgrading.

 

It's a 7/11 naked with a k5 rear shock so I'm not too concerned with keeping parts standard or period unless the forks would really perform being reworked?

 

Thanks again for the replies guys, heavy appreciate them.  

 

[dupersunc]

 Stock forks and brakes, just 9.5 springs and a set of braided lines. 

Don't look very Gucci though. : )

Edited October 16, 2017 by dupersunc

[Oilyspanner]

Thanks for the video D.sunc !    always like a bit of GSXR action ..... are you on a bike with 1100 engine and a 6 speed box ? - gaps between the gears seem different - could just be getting old and senile though !

The 750 Showa usd forks were brilliant, much better action than the 1100's - team Yoshi raced with the 4 pot Nissins for a few seasons -  make sure the pistons move freely and aren't crudded  up, the late radial master cylinders work really well with the 4 pots, EBC HH pads work really well and SBS too (for road work)

[dupersunc]

4 hours ago, Oilyspanner said:

Thanks for the video D.sunc !    always like a bit of GSXR action ..... are you on a bike with 1100 engine and a 6 speed box ? - gaps between the gears seem different - could just be getting old and senile though !

The 750 Showa usd forks were brilliant, much better action than the 1100's - team Yoshi raced with the 4 pot Nissins for a few seasons -  make sure the pistons move freely and aren't crudded  up, the late radial master cylinders work really well with the 4 pots, EBC HH pads work really well and SBS too (for road work)

No, just a stock 1127, with 14/48 gearing.   

Building a 1157, with dot head and 6speed box to go in a 750k chassis currently.  That will run stock 750L forks and brakes but a Brembo radial master cylinder.

Edited October 17, 2017 by dupersunc

[R1guy]

Brembo rcs, or oe? @dupersunc

[dupersunc]

1 hour ago, R1guy said:

Brembo rcs, or oe? @dupersunc

RCS.